Don't listen to these people.
Obviously, people that say a character is bad because of this or that stat are just people that fail at SRPG.
I realized that most vocal people about FE games actually don't know how to use even basic tactic and strategy, and end up getting destroyed because they only know about brute force.
I've recently watched someone play RD on YouTube, the first chapter, and two things were obvious : he was playing on easy, thank god, as he was making stupid moves upon stupid moves. Even in normal made, he would have been wiped out.
Usually, when someone tells you a unit is shit because of some stat, that's because he fails at SRPG.
Like in PoR, where I heard how useless Mist is, yet I never got a problem leveling her.
I started RD on normal just to see, and I tried a casual style of play like in the video I saw : I was wiped out. Now, playing like I'm used to play, no difficulty at all.
RD is far less forgiving for tactic AND strategic errors, so I understand why people say it's so hard.
This is understandable, when you try to trade off using your brain for brute force.
I bet I will have no problem even with Micaiah units, but I haven't played enough to know yet.